(1) Field of the Invention
This invention relates to engine brakes from use in connection with internal combustion engines of the spark ignition or compression ignition type. More particularly, the invention comprises an improvement in a compression release engine brake designed for use in an engine employing a plurality of exhaust valves for each cylinder.
(2) Prior Art
For many years it has been recognized that vehicles, and particularly trucks, equipped with internal combustion engines of the Otto or Diesel type should be provided with some form of engine retarder in addition to the usual wheel brake. The reason for this is that the momentum of a heavily loaded vehicle descending a long grade may easily overcome the capacity for continuous braking of the wheel braking system. An indication of this condition is the well-known "fading" of the wheel brakes resulting from overheating of the brake linings and drums. Excessive heating may cause permanent damage to the brake lining and drum or even destruction of the lining or drum.
Various types of engine retarders have been developed including hydrokinetic retarders, electrical retarders, compression release engine brakes and exhaust brakes. Each of these types of engine retarder has been described in the book "Retarders For Commercial Vehicles" published by Mechanical Engineering Publications, Ltd. (London, 1974).
The present invention relates particularly to engine retarders of the compression release type in which an engine is converted temporarily into an air compressor by opening the exhaust valves near the end of the compression stroke of the engine. By so opening the exhaust valves out of sequence, the energy used to compress air in the cylinder is released through the exhaust system instead of being recovered during the power stroke of the engine. This energy, known as the retarding horsepower, may be a substantial portion of the power ordinarily developed by the engine during a fueling mode of operation and is effective as a supplemental braking system. The Jacobs engine brake to which the present invention is specifically applicable is described in detail at pp. 23-30 of the publication "Retarders For Commercial Vehicles" referred to above and is described generally in the Cummins U.S. Pat. No. 3,220,392.